Method for identifying changes in signal frequencies emitted by a stylus interacting with a digitizer sensor

ABSTRACT

A method for dynamically updating at least one pre-defined value of a parameter used to identify at least one operational mode of an object for user interaction with a digitizer sensor during interaction with the digitizer sensor comprises detecting signal outputs from a plurality of sensing elements of a digitizer sensor during user interaction with the digitizer sensor; characterizing a pattern formed by the signal outputs from the plurality of sensing elements; identifying a pre-defined event associated with an operational mode of the object based on the pattern; determining a value of the parameter from the signal outputs in response to identification of the pre-defined event; and updating the pre-defined value used to identify the operational mode based on the value of the parameter determined from the identified event.

RELATED APPLICATION

The present application claims the benefit under section 35 U.S.C.§119(e) of U.S. Provisional Application No. 60/960,365 filed on Sep. 26,2007 which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a touch sensitive digitizer system, andmore particularly to touch sensitive digitizer system having a passivestylus.

BACKGROUND OF THE INVENTION

Touch technologies are commonly used as input devices for a variety ofproducts. The usage of touch devices of various kinds is growing sharplydue to the emergence of new mobile devices such as Personal DigitalAssistants (PDA), tablet PCs and wireless Flat Panel Display (FPD)screen displays. These new devices are usually not connected to standardkeyboards, mice or like input devices, which are deemed to limit theirmobility. Instead there is a tendency to use touch sensitive digitizersof one kind or another. A stylus and/or fingertip may be used as a userinteraction.

U.S. Pat. No. 6,690,156 entitled “Physical Object Location Apparatus andMethod and a Platform using the same” and U.S. Pat. No. 7,292,229entitled “Transparent Digitizer” both of which are assigned to N-trigLtd., the contents of both which are incorporated herein by reference,describe an electro magnetic method for locating physical objects on aFPD and a transparent digitizer that can be incorporated into anelectronic device, typically over the active display screen. Thedigitizer sensor includes a matrix of vertical and horizontal conductinglines to sense an electric signal. Positioning the physical object at aspecific location on the digitizer provokes a signal whose position oforigin may be detected.

U.S. Pat. No. 7,292,229 further describes a passive electro magneticstylus which is triggered by an excitation coil to oscillate at aresonant frequency. The oscillating signal is sensed by the digitizer.The stylus may operate in a number of different states includinghovering, tip touching, right click mouse emulation, and erasing. Thevarious states may be identified by dynamically controlling the resonantfrequency of the stylus so that the stylus resonates at a differentfrequency in each state or by introducing different modulations to theoscillating signal for each state.

US Patent Application Publication No. 20080128180, entitled “PositionDetecting System and Apparatuses and Methods for Use and ControlThereof” assigned to N-Trig Ltd., the contents of which is incorporatedherein by reference, describes different embodiments for a stylusincluding a pressure sensitive stylus where the oscillation frequency ofthe stylus is modified depending on user applied pressure to the stylus.

U.S. Pat. No. 7,372,455, entitled “Touch Detection for a Digitizer”assigned to N-Trig Ltd., the contents of which is incorporated herein byreference, describes a detector for detecting both a stylus and touchesby fingers or like body parts on a digitizer sensor. The detectortypically includes a digitizer sensor with a grid of sensing conductors,a source of oscillating electrical energy at a predetermined frequency,and detection circuitry for detecting a capacitive influence on thesensing conductor when the oscillating electrical energy is applied, thecapacitive influence being interpreted as a touch.

US Patent Application Publication No. 20050189154, entitled “NoiseReduction in Digitizer Sensor” assigned to N-Trig Ltd., the contents ofwhich are incorporated herein by reference, describes a method for noisereduction in a digitizer, the digitizer comprising a plurality ofdetecting elements for detecting an electromagnetic signal at one of anumber of predetermined frequencies. The detector can be used both forfinger touch sensing and for detection of an electromagnetic stylus. Insome embodiments described, the noise to be reduced originates from afinger or hand that is touching the digitizer during stylus detection.The method includes sampling at least two detecting elementssubstantially simultaneously to obtain outputs therefrom, and reducingthe output on one of said two elements in accordance with the output onthe other of said elements at a frequency other than a pre-determinedfrequency associated with the stylus.

SUMMARY OF THE INVENTION

An aspect of some embodiments of the invention is the provision of amethod for dynamically determining signal frequencies associated withdifferent operational modes of a passive stylus. According to someembodiments of the present invention, there is provided a method fordynamically determining signal frequencies associated hovering mode of astylus while interacting with a digitizer sensor.

An aspect of some embodiments of the present invention is the provisionof a method for dynamically updating at least one pre-defined value of aparameter used to identify at least one operational mode of an objectfor user interaction with a digitizer sensor during interaction with thedigitizer sensor, the method comprising: detecting signal outputs from aplurality of sensing elements of a digitizer sensor during userinteraction with the digitizer sensor; characterizing a pattern formedby the signal outputs from the plurality of sensing elements;identifying a pre-defined event associated with an operational mode ofthe object based on the pattern; determining a value of the parameterfrom the signal outputs in response to identification of the pre-definedevent; and updating the pre-defined value used to identify theoperational mode based on the value of the parameter determined from theidentified event.

Optionally the method comprises identifying the operational mode of theobject with the updated pre-defined value.

Optionally, the object is configured for operating in a plurality ofoperational modes.

Optionally, the plurality of operational modes is selected from a groupincluding: hovering, tip touching, right mouse click emulation, anderasing.

Optionally, the pattern formed by the signal outputs is a pattern ofsignal amplitudes from the plurality of the sensing elements.

Optionally, the pattern of amplitudes is characterized by at least oneratio between amplitudes formed by the signal outputs.

Optionally, the ratio is a ratio between highest amplitude and signaloutput amplitude of at least one contiguous sensing element.

Optionally, identifying the pre-defined event includes comparing the atleast one ratio to a pre-defined threshold.

Optionally, the operational mode associated with the pre-defined eventis a hovering operational mode.

Optionally, the pre-defined event is hovering of the object above apre-defined height from the digitizer sensor.

Optionally, the method comprises estimating a height of object above thedigitizer sensor from the pattern of amplitudes.

Optionally, the height is a function of the at least one ratio andpre-defined coefficients.

Optionally, the method comprises determining at least two ratios betweenamplitudes formed by the signal outputs, wherein the at least two ratiosare configured to resolve ambiguity between patterns of signalamplitudes that are a function of a height of the object above thedigitizer sensor and patterns of signal amplitudes that are a functionof a distance between a sensing element closest to the object and theposition of the object on a surface of the digitizer sensor.

Optionally, the pre-defined event is hovering of the object between afirst pre-defined minimum height and a second pre-defined maximum heightabove the digitizer sensor.

Optionally, identifying a predefined event includes determining thevariance in the frequency of the signal outputs over a plurality ofcycles of sampling the digitizer sensor outputs.

Optionally, the object is selected from a group including: stylus,token, and game piece.

Optionally, the parameter is the frequency of the signal outputs.

Optionally, the object includes a passive resonant circuit configured totransmit a signal in response to a triggering pulse.

Optionally, the resonant circuit is configured for resonating at adifferent frequency for each operational mode.

Optionally, the method comprises matching the triggering frequency of anexcitation coil surrounding the digitizer sensor to an updated frequencyvalue.

Optionally, the value of frequency used to identify that at least oneoperational mode is updated based on values of frequencies determinedover a plurality of cycles of sampling the digitizer sensor outputs.

Optionally, the method comprises updating pre-defined values of theparameter used to identify other operational modes based on thedetermined value of the parameter determined in response toidentification of the pre-defined event.

Optionally, the method comprises adjusting the change in the valuerequired to switch between operational modes identification of thepredefined event.

Optionally, the object includes a resonant circuit and at least onecapacitor connected in parallel to the resonant circuit via a usercontrollable switch, and wherein an operational mode of the object isselected by activating the switch.

Optionally, the object is a pressure sensitive stylus sensitive topressure applied to a tip of the stylus.

Optionally, the pressure sensitive stylus includes a resonant circuit,wherein the resonant circuit includes a variable element and wherein theelement is varied in response to varying pressure applied on the tip ofthe stylus.

Optionally, each sensing element is associated with a position on thedigitizer sensor.

Optionally, the sensing elements include a grid of conductive lines.

An aspect of some embodiments of the present invention is the provisionof a method for identifying that an object configured for interactingwith a digitizer sensor is hovering over the digitizer sensor, themethod comprising: detecting the presence of object in the vicinity ofthe digitizer sensor from detected signal outputs obtained from aplurality of sensing elements of the digitizer sensor; determining atleast one ratio between amplitudes of the signal outputs; andidentifying that the object is hovering based on the at least one ratio.

Optionally, the at least one ratio is a ratio between the highestamplitude and amplitude of a signal output of at least one contiguoussensing element.

Optionally, the method comprises determining a height of the objectabove the digitizer sensor based on the pattern of amplitudes.

Optionally, the method comprises identifying hovering in response to thedetermined height.

Optionally, the method comprises identifying that the object is hoveringfor a height above a pre-defined minimum height.

Optionally, the method comprises identifying that the object is hoveringfor a height below a pre-defined maximum height.

Optionally, the height determined is a qualitative height.

Optionally, the qualitative measure for height includes low hovering,medium hovering and high hovering of the object.

Optionally, the height is a function of the at least one ratio andpre-defined coefficients.

Optionally, the method comprises determining at least two ratios betweenamplitudes formed by the signal outputs, wherein the at least two ratiosare configured to resolve ambiguity between patterns of signalamplitudes that are a function of a height of the object above thedigitizer sensor and patterns of signal amplitudes that are a functionof a distance between a sensing element closest to the object and theposition of the object on a surface of the digitizer sensor.

Optionally, the object is selected from a group including: stylus,token, and game piece.

Optionally, the object interacts with the digitizer sensor in aplurality of operational modes.

Optionally, the plurality of operational modes includes at least one ofhovering operation mode, object touching operational mode, right mouseclick emulation, and erasing.

Optionally, the object includes a passive resonant circuit configured totransmit a signal in response to a triggering pulse.

Optionally, the resonant circuit is configured for resonating at adifferent frequency for each operational mode.

Optionally, the object includes a resonant circuit and at least onecapacitor connected in parallel to the resonant circuit via a usercontrollable switch, and wherein an operational mode of the object isselected by activating the switch.

Optionally, the object is a pressure sensitive stylus sensitive topressure applied to a tip of the stylus.

Optionally, the pressure sensitive stylus includes a resonant circuit,wherein the resonant circuit includes a variable element and wherein theelement is varied in response to varying pressure applied on the tip ofthe stylus.

Optionally, each sensing element is associated with a position on thedigitizer sensor.

Optionally, the sensing elements include a grid of conductive lines.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

Implementation of the method and/or system of embodiments of theinvention can involve performing or completing selected tasks manually,automatically, or a combination thereof. Moreover, according to actualinstrumentation and equipment of embodiments of the method and/or systemof the invention, several selected tasks could be implemented byhardware, by software or by firmware or by a combination thereof usingan operating system.

For example, hardware for performing selected tasks according toembodiments of the invention could be implemented as a chip or acircuit. As software, selected tasks according to embodiments of theinvention could be implemented as a plurality of software instructionsbeing executed by a computer using any suitable operating system. In anexemplary embodiment of the invention, one or more tasks according toexemplary embodiments of method and/or system as described herein areperformed by a data processor, such as a computing platform forexecuting a plurality of instructions. Optionally, the data processorincludes a volatile memory for storing instructions and/or data and/or anon-volatile storage, for example, a magnetic hard-disk and/or removablemedia, for storing instructions and/or data. Optionally, a networkconnection is provided as well. A display and/or a user input devicesuch as a keyboard or mouse are optionally provided as well.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 shows a simplified block diagram of a digitizer system inaccordance with some embodiments of the present invention;

FIG. 2 shows a simplified diagram of pairs of conductive lines of adigitizer sensor that are input to a differential amplifier inaccordance with some embodiments of the present invention;

FIG. 3 shows a simplified circuit diagram of a pressure sensitive styluscapable of resonating at different frequencies in accordance with someembodiments of the present invention;

FIGS. 4A and 4B show simplified block diagrams of two exemplarymechanical structures for a pressure sensitive stylus in accordance withsome embodiments of the present invention;

FIG. 5 shows an exemplary flow chart of a method for selecting a signalduring user interaction with the stylus from which an updated hoverfrequency can be determined in accordance with some embodiments of thepresent invention;

FIG. 6 shows an exemplary flow chart of a method for dynamicallyupdating hover frequency in accordance with some embodiments of thepresent invention;

FIG. 7 shows an exemplary flow chart of a method for initializing updateparameters in the absence of a stylus event in accordance with someembodiments of the present invention;

FIG. 8 shows an exemplary flow chart of a method for updating frequencyassociated with hover in response to detected height of stylus inaccordance with some embodiments of the present invention;

FIG. 9A shows simplified patterns of signal magnitudes corresponding tohovering at different heights in accordance with some embodiments of thepresent invention;

FIG. 9B shows simplified patterns of signal magnitudes obtained fromdifferential amplifiers connected to pairs of conductive lines, thepatterns corresponding to hovering at different heights in accordancewith some embodiments of the present invention;

FIG. 10 shows an exemplary flow chart of a method for determining astylus' height above a digitizer sensor from a pattern of signalmagnitudes detected on the digitizer sensor in accordance with someembodiments of the present invention; and

FIGS. 11A-11B show simplified graphs of exemplary outputs from threeconductive lines of a sensor for different positions of the stylus alongthe digitizer sensor when the stylus is held at two different heights inaccordance with some embodiments of the present invention; and

FIG. 12 shows an exemplary flow chart of a method for determining astylus' height above a digitizer sensor and its position in relation toconductive lines on the digitizer sensor from a pattern of signalmagnitudes detected on the conductive lines of digitizer sensor inaccordance with some embodiments of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention relates to a touch sensitive digitizer system, andmore particularly to touch sensitive digitizer system having a passivestylus.

An aspect of some embodiments of the present invention is the provisionof methods for dynamically determining and adjusting the frequency usedto identify each operational mode of a stylus. Operational modes maytypically include, hovering, tip touching, right mouse click emulationand erasing. According to some embodiments of the present invention, thestylus is designed to resonate at unique predefined frequencies duringeach of its operation modes in response to an excitation signal. Signalstransmitted by the stylus are picked by the digitizer sensor anddeciphered to track the position of the stylus and determine its mode ofoperation. Typically, the mode of operation is determined based on thefrequency of the signals picked up by the digitizer sensor, e.g.frequency of peak output. Typically, the excitation frequency used totrigger the stylus is updated based on the determined mode of operationto match the current resonant frequency of the stylus.

According to some embodiments of the present invention, the stylus isdesigned to change its frequency of transmission in response to pressureapplied to the stylus tip e.g. during a tip touching operational mode,and/or in response to a user activating switches along the length of thestylus, e.g. during an erase operational mode. Mechanical and/orelectrical changes that occur due to applying pressure on the tip and/oractivating one or more switches alter the resonant circuitcharacteristics and thereby the resonant frequency output of the circuitin the stylus. A hovering mode of operation corresponds to a mode whileno pressure is applied on the tip and no user activated switches areactivated.

Typically, during manufacturing, the resonant frequency associated witheach operational mode is determined, calibrated and recorded in thedigitizer system's memory. Recorded frequencies are used to identifyoperational modes of a stylus during interaction with the digitizersensor. However, the inventors have found that over time and with use,the resonant frequencies emitted by the stylus when operating at thedifferent operation modes may change, e.g. drift. In some exemplaryembodiments, characteristics of the resonant circuits may be altered dueto mechanical wear in the stylus with use or due to environmentalchanges, e.g. changes in temperature and/or humidity.

The inventors have found that unpredicted changes in the emittedfrequencies may lead to incorrectly identifying the operation mode ofthe stylus and thereby incorrectly interpreting user input to the host.For example mechanical wear and environmental changes (e.g. thermalchanges) may lead to a stylus emitting a signal at a frequencyoriginally defined for a tip touching operational mode while the stylusis actually hovering over the digitizer sensor.

An aspect of some embodiments of the present invention is the provisionof methods for identifying at least one pre-defined event or state in anoperational mode of the stylus and learning the frequency for thatoperation mode from output signals sampled during that identified event.

The inventors have found that an event where a stylus is hovering at asubstantial height over a digitizing surface can be distinguished fromevents where the stylus is touching the digitizing surface and/orhovering close to the digitizing surface based on patterns formed fromoutputs obtained from conductive lines of a digitizer sensor. In someexemplary embodiments, the patterns are formed from signal amplitudes ofthe output. As used herein, the height of the stylus and/or the stylustip refers to the distance between the digitizing surface and the stylustip. The inventors have found that the pattern of signal amplitudesformed in response to a stylus tip touching the digitizer sensor and/orclose to the digitizer sensor, is a sharp peak around the tip touch areawhile the pattern formed in response to a stylus hovering at pre-definedheights above the digitizer sensor, is a wider peak whose height isinversely related the height of the hovering, e.g. sharp peak for zeroor low heights and shallow peak for heights above a pre-definedthreshold.

According to some embodiments of the present invention, identificationof the at least one event is based on detected patterns of signalamplitudes obtained from conductive lines of a digitizer sensor. In someexemplary embodiments, a pre-defined event includes a stylus hoveringover a digitizer sensor at a height between two pre-defined thresholds.In some exemplary embodiments, a pre-defined event includes a stylushovering over a digitizer sensor at a height above a pre-definedthreshold.

According to some embodiments of the present invention, as thefrequencies of the passive stylus drifts, methods that are not solelybased on frequency detection are required to verify the operational modeof the stylus and determine an updated frequency associated with thatmode. According to some embodiments of the present invention, once apre-defined event is identified, the frequency of the output signalsobtained for that event is detected and used to update the frequency ofan operational mode associated with that event. According to embodimentsof the present invention, operational modes of the stylus are detectedfrom updated frequencies defined for at least one operational mode.

The inventors have found that changes in the resonant circuitcharacteristics typically have a global effect on all of the operationalmodes. So that if a frequency associated with a particular operationalmode has been found to change, e.g. has shifted, that same shift cantypically be applied to the frequencies associated with the otheroperational modes. Typically, frequency of the stylus signal for eachoperational mode is altered in relation to a defined hover frequency, sothat if the hover frequency drifts in one direction, frequenciesassociated with other operational modes will also have a similar driftin that direction. Optionally, if a frequency associated with aparticular operational mode has been found to change, e.g. has shifted,a relative shift which is proportional to the frequency can typically beapplied to the frequencies associated with the other operational modes.As used herein, hover frequency is defined as the frequency transmittedby the stylus while no pressure is applied to the stylus tip and whileno operational mode switch is activated.

An aspect of some embodiments of the present invention is the provisionof methods for identifying an event or state in a hovering operationalmode and updating frequencies associated with each of the operationalmode based on the frequencies detected from signals obtained during theidentified hover event. In some exemplary embodiments, the pre-definedfrequencies for each of the operation modes are updated substantiallycontinuously during operation of the digitizer sensor. In some exemplaryembodiments, the pre-defined frequencies for each of the operation modesare updated periodically, e.g. at pre-defined time intervals duringoperation and/or once during start-up of the digitizer sensor.

According to some embodiments of the present invention, the hover eventis identified based on a calculated height approximation of the stylustip above the digitizer sensor. In some exemplary embodiments, heightapproximation is based on analysis of patterns of signal amplitudesoutputs from a plurality of sensing elements of the digitizer sensor.

According to some embodiments of the present invention, values of ratiosbetween magnitudes of signal output from a plurality of sensing elementsare used as an indication of the height and width of a peak formed inresponse to the presence of a stylus. In some exemplary embodiments, aratio is calculated between a sum of magnitudes obtained from apre-defined number of sensing elements, e.g. 4 sensing elements, havingthe largest magnitudes and a sum total of magnitudes obtained from allsensing elements in a pre-defined area. According to some embodiments ofthe present invention, the ratio is associated with a height of thestylus above the digitizer sensor. In some exemplary embodiments, aheight greater than zero, defines an event from which hover frequencycan be detected. Typically, the sensing elements with the largestmagnitude outputs are chosen from a common vicinity. Typically, thepre-defined area is the entire area of the digitizer sensor. In someexemplary embodiments a polynomial is defined relating hovering heightto the calculated ratio. Typically, the coefficients of the polynomialare determined from statistically analysis of experimental results.

In some exemplary embodiments, two ratios are calculated and used toobtain approximation of both the hovering height and the position of thestylus on the digitizer sensor surface. A first ratio is between thehighest magnitude output and the magnitude output from the closestcontiguous sensing element, e.g. the closest sensing element to the leftof the sensing element with the highest output. The second ratio isbetween two sensing elements closest to the sensing element with thehighest output. In some exemplary embodiments, an estimated position andheight is determined from the two ratios based on a looked up tableconstructed from experimental results. Typically, the look-up table isspecific for each type of digitizer system and/or each type of stylus.

According to some embodiments of the present invention, a pre-definedevent from which hover frequency can be determined is identified inresponse to the existence of a plurality of conditions. In someexemplary embodiments, the plurality of conditions requires that theratio between the highest signal amplitude output and the second signalhighest amplitude output is above a pre-defined threshold. In someexemplary embodiments, the plurality of conditions requires that theratio between the highest signal amplitude output and the third highestsignal amplitude output is above a pre-defined threshold. In someexemplary embodiments, the plurality of conditions requires that thehighest signal amplitude output is above a predefined threshold.

The inventors have found that variance of frequency content of ahovering signal typically increases for hovering above a pre-definedthreshold. This is typically attributed to accumulated noise, e.g. alower Signal to Noise Ratio (SNR), associated with hovering heightsabove a pre-defined threshold. In some exemplary embodiments, theplurality of conditions requires that the variance of the frequencycontent of the hovering signal be below a pre-determined variance sothat only hovering events below a pre-defined maximum height are used tolearn an updated frequency associated with hovering. In some exemplaryembodiments, the plurality of conditions requires that the frequencyoutput of the detected signal does not stray from the pre-defined hoverfrequency more than a pre-defined amount.

According to some embodiments of the present invention, the hoverfrequency is updated with weighted averages of previously detected hoverfrequencies. According to some exemplary embodiments, a parameterindicating a confidence level that the current hover frequency is thetrue hover frequency is determined. In some exemplary embodiments, theconfidence level is directly related to the number of frequency updatesincluded in the weighted average. In some exemplary embodiments, theconfidence level is implemented to define a change in detected frequencyrequired to switch operational modes, e.g. switch between hover and tiptouching operational mode. As used herein tip touching operation moderefers to an operational mode defined by the stylus' tip touching thedigitizing surface. In some exemplary embodiments, tip touchingoperational mode may be referred to as object touching operational mode.In some exemplary embodiments, for high confidence levels, a relativelysmall change in frequency is enough to initiate a change in operationalmodes, e.g. 100 Hz. Lowering the change in frequency required makes thestylus more sensitive so that a small change in pressure applied to thestylus is enough to switch operational modes. In some exemplaryembodiments, for low confidence levels, a relatively larger change infrequency is required to initiate a change in operational modes, e.g.200 Hz. Increasing the change in detected frequency required makes thestylus less sensitive so that the stylus has to be lifted from thedigitizer sensor by a significant amount to switch to hoveringoperational mode and/or a significant pressure needs to be applied tothe stylus needs to switch to tip touching operational mode. Typicallylow and high confidence levels are determined by pre-defined thresholds.

The inventors have also found that as the resonant circuitcharacteristics of a passive stylus change, a mismatch between theexcitation signal used to trigger the stylus and the resonant circuitfrequency of the stylus may develop. As a result of this mismatch,energy delivered to the stylus is compromised and thereby the strengthof the signal that can be transmitted by the stylus is reduced. In someexemplary embodiments, the excitation frequency used to trigger thestylus is updated based on the determined shifts in the frequenciesassociated the current operational mode. In some exemplary embodiments,the search frequency used for Discrete Fourier Transform (DFT)calculation is updated based on the determined shifts in the frequenciesassociated the current operational mode.

It is noted that although some embodiments of the present invention aredescribed in reference to a pattern of signal amplitudes, in someexemplary embodiments, other patterns may be used to identify apre-defined event, e.g. a pattern of phase output. It is also noted thatalthough some embodiments of the present invention are described inreference to identifying a pre-defined hover event to update definedfrequencies of operational modes, in some exemplary embodiments otherevents may be identified to update defined frequencies of operationalmodes, e.g. a pre-defined tilting of a user interaction. It is alsonoted that although some embodiments of the present invention aredescribed in reference to a stylus user interaction, in some exemplaryembodiments other objects may be used for user interaction, e.g. a tokenand/or a game piece. It is also noted that although some embodiments ofthe present invention are described in reference to identifyingoperational modes based on defined frequencies, the methods describedherein can be applied to digitizer systems that identify operationalmodes of a user interaction by other methods, e.g. by phase output of asignal or amplitude of a signal.

Referring now to the drawings, FIG. 1 illustrating an exemplarysimplified block diagram of a digitizer system in accordance with someembodiments of the present invention. The digitizer system 100 may besuitable for any computing device that enables interactions between auser and the device, e.g. mobile computing devices that include, forexample, FPD screens. Examples of such devices include Tablet PCs, penenabled laptop computers, tabletop computer, PDAs or any hand helddevices such as palm pilots and mobile phones or other devices thatfacilitate electronic gaming. According to some embodiments of thepresent invention, the digitizer system comprises a sensor 12 includinga patterned arrangement of conducting lines, which is optionallytransparent, and which is typically overlaid on a FPD. Typically sensor12 is a grid based sensor including horizontal and vertical conductinglines.

According to some embodiments of the present invention, circuitry isprovided on one or more PCB(s) 30 positioned around sensor 12. Accordingto some embodiments of the present invention PCB 30 is an ‘L’ shapedPCB. According to some embodiments of the present invention, one or moreASICs 16 positioned on PCB(s) 30 comprises circuitry to sample andprocess the sensor's output into a digital representation. The digitaloutput signal is forwarded to a digital unit 20, e.g. digital ASIC unitalso on PCB 30, for further digital processing. According to someembodiments of the present invention, digital unit 20 together with ASIC16 serves as the controller of the digitizer system and/or hasfunctionality of a controller and/or processor. Output from thedigitizer sensor is forwarded to a host 22 via an interface 24 forprocessing by the operating system or any current application.

According to some embodiments of the present invention, digital unit 20together with ASIC 16 includes memory and/or memory capability. Memorycapability may include volatile and/or non-volatile memory, e.g. FLASHmemory. In some embodiments of the present invention, the memory unitand/or memory capability, e.g. FLASH memory is a unit separate from thedigital unit 20 but in communication with digital unit 20.

According to some embodiments of the present invention, sensor 12comprises a grid of conductive lines made of conductive materials,optionally Indium Tin Oxide (ITO), patterned on a foil or glasssubstrate. The conductive lines and the foil are optionally transparentor are thin enough so that they do not substantially interfere withviewing an electronic display behind the lines. Typically, the grid ismade of two layers, which are electrically insulated from each other.Typically, one of the layers contains a first set of equally spacedparallel conductors and the other layer contains a second set of equallyspaced parallel conductors orthogonal to the first set. Typically, theparallel conductors are input to amplifiers included in ASIC 16.Optionally the amplifiers are differential amplifiers.

Typically, the parallel conductors are spaced at a distance ofapproximately 2-8 mm, e.g. 4 mm, depending on the size of the FPD and adesired resolution. Optionally the region between the grid lines isfilled with a non-conducting material having optical characteristicssimilar to that of the (transparent) conducting lines, to mask thepresence of the conducting lines. Optionally, the ends of the linesremote from the amplifiers are not connected so that the lines do notform loops.

Typically, ASIC 16 is connected to outputs of the various conductors inthe grid and functions to process the received signals at a firstprocessing stage. As indicated above, ASIC 16 typically includes anarray of amplifiers, e.g. differential amplifiers, to amplify thesensor's signals. Additionally, ASIC 16 optionally includes one or morefilters to remove frequencies that do not correspond to frequency rangesused for excitation and/or obtained from objects used for userinteractions. Optionally, filtering is performed prior to sampling. Thesignal is then sampled by an A/D, optionally filtered by a digitalfilter and forwarded to digital ASIC unit 20, for further digitalprocessing. Alternatively, the optional filtering is fully digital orfully analog.

According to some embodiments of the invention, digital unit 20 receivesthe sampled data from ASIC 16, reads the sampled data, processes it anddetermines and/or tracks the position of physical objects, such as astylus 44, a finger 46, and/or an electronic tag touching the digitizersensor from the received and processed signals. According to someembodiments of the present invention, digital unit 20 determines thepresence and/or absence of physical objects, such as stylus 44, and/orfinger 46 over time. In some exemplary embodiments of the presentinvention hovering of an object, e.g. stylus 44, finger 46 and hand, isalso detected and processed by digital unit 20. According to someembodiments of the present invention, hovering and touching elements aredifferentiated by analysis of signal strength and/or signal frequency.Calculated position is sent to the host computer via interface 24.

According to some embodiments, digital unit 20 produces and controls thetiming and sending of a triggering pulse to be provided to an excitationcoil 26 that surrounds the sensor arrangement and the display screen.The excitation coil provides a trigger pulse in the form of an electricor electromagnetic field that excites passive circuitry in stylus 44 orother object used for user interaction to produce a response from thestylus that can subsequently be detected. Typically, to trigger apassive stylus, digital 20 provides a triggering pulse in a frequencythat matches the resonant frequency of the stylus. According to someembodiments of the present invention, the frequency of the trigger pulseis updated in response to detected changes in the characteristics ofcircuitry in the stylus. Typically, the changes in the resonantfrequency of the stylus circuit are small, so that a response from thestylus may still be achieved despite a mismatch between the frequency ofthe triggering pulse and the frequency of the stylus resonant circuit.Additionally, the excitation signal provided by the excitation coiltypically includes side lobes so it includes a range of frequencieswithin a frequency band surrounding the frequency of the trigger pulse.Typically, the frequency output of the stylus is detected as theresponse to a triggering pulse decays so that the stylus is oscillatingat its own resonant frequency as opposed to the resonant frequency ofthe excitation coil. Typically, a mismatch resonant frequency of thestylus may be detected within the frequency bandwidth of the stylusoutput. In some exemplary embodiments, the frequency output of thesignal is detected by one or more of ASIC units 16 or digital unit 20and updates to the frequency of the trigger pulse may be made based onthe detected frequency.

According to some embodiments, digital unit 20 produces and sends atriggering pulse to at least one of the conductive lines. Typically thetriggering pulses and/or signals are analog pulses and/or signals.According to some embodiments of the present invention, the triggeringpulse and/or signal implemented may be confined to one or morepre-defined frequencies, e.g. 18 KHz or 20-40 KHz. In some exemplaryembodiments, finger touch detection is facilitated when sending atriggering pulse to the conductive lines.

According to some embodiments of the invention, host 22 includes atleast a memory unit 23 and a processing unit 25 to store and processinformation obtained from ASIC 16, digital unit 20. According to someembodiments of the present invention memory and processing functionalitymay be divided between any of host 22, digital unit 20, and/or ASIC 16or may reside in only one of them and/or there may be a separated unitconnected to at least one of host 22, digital unit 20, and ASIC 16.According to some embodiments of the present invention, one or moretables and/or databases may be stored to record statistical data and/oroutputs, e.g. images or patterned outputs of sensor 12, sampled by ASIC16 and/or calculated by digitizer unit 20. In some exemplaryembodiments, a database statistical data from sampled output signals maybe stored. Data and/or signal values may be stored in volatile andnonvolatile memory. According to some embodiments of the presentinvention, data and/or signal values may be stored as tables of spatialoutput of the digitizer sensor and/or differential amplifier output ofthe digitizer sensor. According to some embodiments of the presentinvention outputs are recorded after Discrete Fourier Transformationand/or filtering, e.g. after low pass and/or band-pass filtering.

Reference is now made to FIG. 2 showing a simplified diagram of pairs ofconductive lines of a digitizer sensor that are input to a differentialamplifier in accordance with some embodiments of the present invention.According to some embodiments of the present invention, parallelnon-adjacent conductive lines 210 and 220 of sensor 12 are input todifferential amplifier 240. According to some embodiments of the presentinvention, output 250 from a differential amplifier 240 is interrogatedto determine if there is an input signal derived from touch and/orhovering on either of lines 210 and 220. Similarly, outputs ofdifferential amplifiers associated with neighboring parallel lines andwith orthogonal conductive lines of the grid are also interrogated.Typically, separation between two contiguous conductive lines may spanbetween 1-6 mm and conductive lines 210 and 220 may typically beseparated by at least two conductive lines positioned between them, e.g.2-6 lines between them. The differential amplifier 240 amplifies thepotential difference developed between conductive lines 210 and 220.ASIC 16 and digital unit 20 process the amplified signals from theconductive lines to identify a touch or hovering event occurring on oneof the lines. According to some embodiments, differential amplifiers areused to diminish the affect of steady state signals that may appear invicinities of the digitizer sensor.

Digitizer systems used to detect stylus and/or finger tip location maybe, for example, similar to digitizer systems described in incorporatedU.S. Pat. No. 6,690,156, U.S. Pat. No. 7,292,229 and/or U.S. Pat. No.7,372,455. Additionally, styluses may be, for example, similar tostyluses described in incorporated US Patent Application Publication No.20080128180. Embodiments of the present invention will also beapplicable to other digitizer systems known in the art, depending ontheir construction. Embodiments of the present invention will also beapplicable to other digitizer sensors known in the art, e.g. sensorscomprising loop coils.

Reference is now made to FIG. 3 showing a simplified circuit diagram ofa pressure sensitive stylus capable of resonating at differentfrequencies in accordance with some embodiments of the presentinvention. According to some embodiments of the present invention, thestylus 300 is a passive stylus including an inductor 321 and a 322capacitor to form a basic resonant circuit from which stylus 300 istriggered. In some exemplary embodiments, inductor 321 is a variableinductor whose inductance is varied in response to pressure applied tothe tip 306 of stylus 300. In response to pressure, inductance isaltered so that the resonant frequency of the circuit may eitherincrease or decrease. The varying capability of inductor 321 will befurther described herein below, e.g. in reference to FIGS. 4A-4B.According to some embodiments of the present invention, stylus 300includes additional capacitors 323 and 324 that are connected inparallel to capacitor 322 by one or more operational mode switches 325and 326. Typically, switches 325 and 326 are manipulated by the user toselect different modes of stylus operation, e.g. erasing and right clickmouse emulation. In some exemplary embodiments, one or more switchespositioned on a frame of stylus 300 are used to control switches 325 and326. In some exemplary embodiments, a rocker switch is positioned on theframe and used to control switches 325 and 326. Optionally more than twocapacitors are connected in parallel to capacitor 322 and additionaloperational modes are defined and controlled by an external switch, e.g.rocker switch. In response to activating one or more of switches 325 and326, capacitors 323 and/or 324 introduce changes to the basic resonantcircuit and thereby introduce changes to the resonant frequency of thecircuit. Typically, the total capacitance of all capacitors connected tothe circuit together with inductor 321 determines the resonancefrequency of the resonance circuit so that stylus 300 has a uniqueresonant frequency for each operation mode. Typically, stylus 300 ispassive and its resonant circuit oscillates in response to an excitationsignal provided by an external source, e.g. excitation coil 26 thatincludes the resonant frequency of the stylus's circuit.

In some exemplary embodiments, one end of the resonant circuit iselectrically connected to the stylus tip 306, which preferably comprisesa conductive material while the other end is electrically connected to aframe 304, which likewise comprises conductive material. An electricfield 308, synchronized to the resonant circuit oscillations, is formedin a gap 110 located between the tip 306 and the frame 304. Thegeometric dimensions of the gap and the consequent field are relativelysmall so that the field source can be substantially close to the stylustip and thereby provide a concentrated signal at the tip.

Reference is now made to FIGS. 4A-4B showing simplified block diagramsof two exemplary mechanical structure for a pressure sensitive stylus inaccordance with some embodiments of the present invention. In FIG. 4A,stylus 400 includes a frame 420 with a tip 409 that is movable in thedirection of its longitudinal axis. In some exemplary embodiment, afirst end of a rod 404 is secured to movable tip 409 via holder body 410and a spring 405. In some exemplary embodiments, spring 405 ispositioned around holder body 410 and secured to frame 420 to apply aspring force on tip 409. Optionally, a mechanical stopper is positionedat one end of the spring to prevent application of pressure that is outof the dynamic range that can be sensed by the digitizer.

According to some embodiments of the present invention, a first ferriteobject 401 is fixed to a frame 420 substantially surrounds rod 404. Insome exemplary embodiments, first ferrite object 401 is a cylindricalobject including a bore through which rod 404 is positioned. Typically,a coil 402 providing inductance to resonant circuit 300 is woundedaround first ferrite object 401. According to embodiments of the presentinvention, coil 402 serves as a receiving coil that picks up currentsinduced by external excitation coil 26 creating a magnetic field. Thepresence of ferrite object 401 serves to increase energy transferbetween the external excitation coil 26 and coil 402 by strengtheningthe magnetic field. According to some embodiments of the presentinvention, a second ferrite object 403 is secured over a second end ofrod 404 so that second ferrite object 403 together with rod 404 ismovable with respect to first ferrite object 401. According to someembodiments of the present invention, the varying inductance 321provided by coil 402 is a function of the distance between the first andsecond ferrite objects. Typically, the presence of second ferrite objectwithin the magnetic field produced by coil 402, serves to reduce thelength of the magnetic field lines created by coil 402 and therebyincrease the inductance. This effect is increased as the second ferriteobject approaches coil 402 and first ferrite object 401 and is decreasedas the second ferrite object is distanced from coil 402 and firstferrite object 401.

In operation, while pressure is applied to tip 409, second ferriteobject 403 is distanced from first ferrite object 401. As the userapplies pressure on tip 409 and overcomes the force applied by thespring, second ferrite object 403 moves along the axis of the tip 409and rod 404 in a direction away from first ferrite object 401, reducingthe inductance. In some exemplary embodiments, the spring applies aforce of approximately 5 to 15 gram-force along the axis of the rod sothat the first and second ferrite are held together while no pressure isapplied to the tip. Optionally, a spacer 406 is positioned between thetwo ferrite objects to form a pre-determined gap between them when nopressure is applied. In some exemplary embodiments, the spacer providinga gap of approximately 50 to 150 μm is used. Optionally, spring 405and/or holder body 410 is manufactured from conductive material and isused to transmit the signal from the resonant circuit to tip 409.

In some exemplary embodiments, the inductance value varies by several mHdue to the change in gap size. The change in inductance results in achange in the frequency of the signal transmitted by the tip. In someexemplary embodiments, the resonant frequency increases as a function ofincreasing pressure.

In some exemplary embodiments, an elastic body 407, e.g. an O-ring ispositioned in between second ferrite object 403 and frame 420, e.g. onhousing 420 in an opposite end from tip 409. In some exemplaryembodiments, a gap 408 of approximately 10-30 μm is formed betweenelastic body 407 and second ferrite object 403 in an initial state whenthere is no pressure applied on tip 409. As the user applies pressure ontip 409, elastic body 407 engages second ferrite object 403 and appliesa force in a direction opposite a pressure applied by a user on tip 409.Typically, as the a user increase pressure on tip 409, the resistanceapplied by elastic body 407 increases due to an increase in surface areaof elastic body contacting second ferrite body 403.

In some exemplary embodiment, the change in frequency due to changes ininductance ranges approximately between 100-200 Hz so that a differencebetween the frequency when no pressure is applied and a frequency whenpressure is applied ranges between 100-200 Hz.

In FIG. 4B, stylus 450 includes a first ferrite object 454 that issecured to a tip 460 and moves together with tip 460 along itslongitudinal axis. Typically, a coil 402 providing inductance toresonant circuit 300 is wounded around first ferrite object 454. Asecond ferrite object 452 is stationary with respect to frame 470 and ispositioned with so that a gap 453 is formed between the first and secondferrite objects while no pressure is applied to tip 460. Duringoperation, while a user applies pressure to tip 460, ferrite object 454approaches second ferrite object 452 and gap 453 between them decreases.The decrease in gap 453 leads to an increase in inductance and thereby adecrease in the resonant frequency transmitted. In some exemplaryembodiments, the resonant frequency decreases as a function ofincreasing pressure. In some exemplary embodiments, the inductancevalues may vary by several 0.1 mH. Optionally, changes in inductancesand resonant frequency may be similar to changes in frequency describedin reference to FIG. 4A.

According to some embodiments of the present invention, duringmanufacturing, frequencies emitted by the stylus for each of theoperational modes are calibrated and the frequency values are stored inthe digitizer system's memory for reference. In some exemplaryembodiments, a frequency corresponding to a hovering operational mode isset at 28 KHz or 29 KHz while tip touch mode is set at 200 Hz below orabove hover mode, depending on the configuration of the stylus used. Insome exemplary embodiments, for systems operating with a stylus similarto stylus 400, tip touch mode is set at 200 Hz above hover mode whilefor systems operating with a stylus similar to stylus 450, tip touchmode is set at 200 Hz below hover mode. During operation, the differentmodes of operation may be identified based on frequency of a signalpicked up from the digitizer sensor.

According to some embodiments of the present invention, while thepresence of a stylus has not been detected, e.g. at a system start-up,the digitizer system operates in a search mode to search for a stylusinteracting with the digitizer sensor. During a search mode, excitationcoil 26 emits trigger pulses and/or oscillates in a plurality offrequencies including the frequencies corresponding to the differentoperational modes of the stylus. According to some embodiments, of thepresent invention, once the stylus is detected, the frequency of thepeak output is determined and the operational mode is identified.According to some embodiments of the present invention, once the stylusis deed and the operational mode is identified, the digitizer systemswitches to tracking mode and digital unit 20, triggers excitation coil26 at the resonant frequency corresponding to the identified operationalmode. According to some embodiments of the present invention, thedigitizer system tracks the position of the stylus during tracking modeusing the triggering frequency corresponding to the resonant frequencyof the stylus for that mode to obtain output. According to someembodiments of the present invention, the system returns to search modewhen the presence of the stylus is lost. In some exemplary embodiments,the presence of the stylus is lost in response to a change in theoperational mode of the stylus.

According to some embodiments of the present invention, during operationof the digitizer system, the digitizer system also tracks any drift inhover frequency and updates frequencies associated with each of theoperational modes of the stylus based on a detected hover frequency whenrequired. As used herein, hover frequency is defined as the frequencytransmitted by the stylus while no pressure is applied to the stylus tipand while no operational mode switch is activated, e.g. while switches325 and 326 are not closed. It is noted that according to embodiments ofthe present invention, the normal state of switches 325 and 326 may beopen or closed. Typically, a hovering operational mode needs to beidentified before changes in hover frequency can be identified. However,since the current hover frequency is not known to the system, it is notpossible to verify that the stylus is in hovering operational mode basedonly on the frequency of the detected signal. According to someembodiments of the present invention, other characteristics of adetected signal are used to verify that the stylus is in a hoveringoperational mode and to verify that the detected hover signal issuitable for tracking a change in hover frequency.

Reference is now made to FIG. 5 showing an exemplary flow chart of amethod for selecting a signal during user interaction with the stylusfrom which an updated hover frequency can be determined in accordancewith some embodiments of the present invention. Upon start-up of thedigitizer system, the digitizer sensor is sampled (block 510) and aquery is made to determine if a stylus is in the vicinity of thedigitizer sensor (block 515). Typically, presence of a stylus isdetected in search mode. According to some embodiments of the presentinvention, a stylus is determined to be in the vicinity of the digitizersensor if one or more digitizer sensor outputs are above a predefinedthreshold for determining the presence of a stylus.

According to some embodiments of the present invention, if the presenceof a stylus is not determined, hover frequency update parameters areinitialized (block 710) as is further described herein, e.g. inreference to FIG. 7. According to some embodiments of the presentinvention, if the presence of a stylus is determined, a pre-definedupper limit on frequencies of detected signals, F_(max), is checked forupdates (block 520). According to some embodiments of the presentinvention, an upper limit on frequencies of detected signals isdetermined for digitizer systems using stylus' similar to stylus 450where hover frequency constitutes the operational mode with the highestfrequency. However, it is noted that similar methods described hereincan be used for stylus' similar to stylus 400 by defining and updating alower limit on frequencies of detected signals, F_(min) instead of anupper limit. This is because for stylus' similar to stylus 400, hoverfrequency constitutes the operational mode with the lowest frequency.

According to some embodiments of the present invention, a maximumfrequency in the detected signal is determined and compared with apreviously defined F_(max), e.g. an F_(max) defined and stored at themanufacturing site, and if the maximum frequency currently detected isfound to be greater than F_(max), F_(max) is updated to the currentmaximum frequency. Fmax is defined as the maximum frequency everdetected in the system since last reset of the system. According to someembodiments of the present invention, F_(max) is determined to limit thepossible frequency that can be associated with hovering.

In some exemplary embodiments, the system detects a presence of fingerand/or palm touch prior to updating F_(max). In some exemplaryembodiments, if a finger and/or a palm are detected, F_(max) is notupdated. In some exemplary embodiments, if a finger and/or a palm aredetected, a noise reduction algorithm is run to remove influences offinger and/or palm touch and F_(max) is updated only if the algorithmcan remove the influences of finger and/or palm touch. In some exemplaryembodiments, the noise reduction algorithm is similar to that describedin incorporated US Patent Application Publication No. 20050189154. Insome exemplary embodiments, F_(max) is only updated if the magnitude ofthe signal from which F_(max) was detected is above a pre-definedthreshold for updating F_(max).

According to some embodiments of the present invention, a query is madeto determine if the current maximum frequency of the signals detecteddiffers from F_(max) by a more than a pre-defined threshold, TH1 (block525). In some exemplary embodiments, for a difference in current maximumfrequency below a pre-defined threshold from F_(max), it is suspectedthat the stylus is not in hover mode and the signals are not acceptedfor learning a new hover frequency (block 560). However, if thedifference in F_(max) is below the pre-defined threshold, additionalconditions are queried to determine if the signals are suitable forlearning a new hover frequency.

The present inventors have found that variance of frequency content of ahover signal increases for hovering above a pre-defined threshold. Thisis typically attributed to accumulated noise, e.g. a lower Signal toNoise Ratio (SNR), associated with hovering heights above a pre-definedthreshold. According to embodiments of the present invention, hoveringevents above a pre-defined threshold are not used for updating frequencydefined for hovering operational modes. According to some embodiments ofthe present invention, the frequency variance of one or more detectedsignals from the digitizer sensor is checked against a threshold andonly if the signals are found to have a variance below the pre-definedthreshold, TH2 the signals accepted as potential signals for learning anew hover frequency (block 530). In some exemplary embodiments, theoutput with the highest magnitude is queried for this purpose. In someexemplary embodiments, the outputs with three of hour highest magnitudesare queried for this purpose.

According to some embodiments of the present invention, an additionalquery is made to determine if one or more of the operational modeswitches are activated (block 535). In some exemplary embodiment thedetected signals are only accepted as potential signals for learning anew hover frequency if all switches are off, e.g. not activated.

According to some embodiments of the invention, the maximum amplitude ofthe detected signals are compared to a pre-defined threshold and only ifthe maximum amplitude detected is above a pre-defined threshold, are thesignals considered as a potential signal for learning a new hoverfrequency (block 540).

According to some embodiments of the present invention, ratios betweendifferent outputs of the sensor are determined and compared tothresholds to determine if a pattern of signal outputs obtained from thedigitizer is typical of patterns obtained during a hovering event wherethe stylus is hovering above a pre-defined height. The present inventorshave found that during hovering above a pre-defined height, the peak inthe amplitude pattern formed by output from the digitizer sensor istypically shallower and wider as compared to the peak formed during tiptouch of the stylus tip and/or lower hovering. According to someembodiments of the present invention, a hovering event where the stylusis hovering above a predefined height is identified by determiningattributes of the peak in the amplitude pattern formed by output fromthe digitizer sensor. According to some embodiments of the presentinvention, one or more parameters are defined to determine a qualitativeand/or quantitative measure of the height and width of the peak in theamplitude pattern formed by output from the digitizer sensor. Accordingto embodiments of the present invention, a hovering event where thestylus is hovering above a pre-defined height is detected based onvalues of the defined parameters.

According to some embodiments of the present invention, a ratio betweenthe maximum amplitude output and the second highest amplitude output iscompared to a pre-defined threshold, TH4 (block 545). In some exemplaryembodiments, TH4 is 5-20, e.g. 10. According to some embodiments of thepresent invention, for ratios smaller than the pre-defined threshold,the signals are determined as potential signals for learning hoverfrequency. In some exemplary embodiments, the maximum and second highestoutputs are required to be obtained from a same vicinity in thedigitizer sensor, e.g. obtained from conductive lines that are within1-5 lines apart.

According to some embodiments of the present invention, an additionalcondition includes that a ratio between the maximum amplitude output andthe third highest amplitude output is below a pre-defined threshold, TH5(block 550). In some exemplary embodiments, the maximum and thirdhighest outputs are required to be obtained from a same vicinity in thedigitizer sensor, e.g. obtained from conductive lines that are within1-5 lines apart.

According to some embodiments of the present invention, if all theconditions for determining that the detected signals are potentialsignals for learning hover frequency are met, an updated hoverfrequency, F_(hover), is determined based on the detected signals (block555). According to some embodiments of the present invention, if one ormore of the defined conditions are not met, hover frequency is notupdated during this sampling cycle (block 560). In some exemplaryembodiments of the present invention, this cycle is repeated for eachset of outputs sampled from the digitizer sensor. In some exemplaryembodiments, this cycle is repeated once for every pre-defined number ofcycles.

Reference is now made to FIG. 6 showing an exemplary flow chart of amethod for dynamically updating hover frequency in accordance with someembodiments of the present invention. According to some embodiments ofthe present invention, hover frequency is updated based on weightedaverages with previously defined hover frequencies using the followingrelationship:F _(hover)=(F _(current) +F _(hover) _(—) _(prev) *W)/(1+W);

Where W equals the number of updates made since system start-up and/orsince detection of the presence of the stylus (block 610); F_(current)is the frequency detected for the currently identified hover signaloutput; and F_(hover) _(—) _(prev) is the previously defined frequencyfor hover. Typically, F_(current) is defined as the frequencycorresponding to the peak signal output for the currently identifiedhover signal output. As W increases, e.g. the number of updates madeincreases, the weight of the previous updates increases therebystabilizing F_(hover). In some exemplary embodiments, as W increases theconfidence level that the defined hover frequency is a true hoverfrequency is increased. If W is less than a pre-defined maximum valueW_(max) (block 615), W is incremented (block 620) and a query is made todetermine if W_(max) has been reached (block 625). In some exemplaryembodiments, W_(max) is set between 8-12, e.g. 10. According to someembodiments of the present invention, when W reaches W_(max), theconfidence level that the defined hover frequency is a true hoverfrequency is high and as a result the change in frequency thresholdrequired for switching between a hover mode and a tip touchingoperational mode is reduced (block 630). In some exemplary embodiments,the frequency threshold required for switching between a hover mode anda tip touching operational mode for high confidence levels of hoverfrequency is approximately 100 Hz while the threshold required duringlow confidence levels is approximately 200 Hz. According to someembodiments of the present invention, while a hover event has beenidentified with a low confidence level more pressure on the tip isrequired before a tip touching operational mode is identified making thesystem less sensitive to changes between hover and tip touch. Accordingto some embodiments of the present invention, while a hover event beenidentified with a high confidence level, less pressure on the tip isrequired for a tip touching operational mode to be identified making thesystem more sensitive to changes between hover and tip touch. Typically,the frequency threshold required for switching between a hover mode anda tip touching operational mode is determined based on the mechanicalstructure and/or circuitry of the stylus. In some exemplary embodiments,once W reaches is maximum value (block 635), hover frequency is notupdated. In some exemplary embodiments, W is set to 0 after apre-defined number of cycles, in response to a system start-up, and/orafter the presence of the stylus is lost.

Reference is now made to FIG. 7 showing an exemplary flow chart of amethod for initializing update parameters in the absence of a stylusevent in accordance with some embodiments of the present invention.According to some embodiments of the present invention, when thepresence of a stylus is not detected, parameters for hover frequencyupdate are initialized (block 710). In some exemplary embodiments,F_(max) is initiated to its original value, e.g. its value set duringcalibration at a manufacturing site (block 715). In some exemplaryembodiments, the original value of F_(max) is defined as 28 KHz and/or29 KHz. In some exemplary embodiments, the original value of F_(max) isdefined as 28 KHz when the frequency for tip touching operational modeis defined to be lower than hovering operational mode. In some exemplaryembodiments, the original value of F_(min) is defined as 29 KHz when thefrequency for tip touching operational mode is defined to be higher thanhovering operational mode. In some exemplary embodiments, initializingF_(max) serves to avoid accumulated error and/or to accommodateintroduction of a stylus other than the stylus previously used.

In some exemplary embodiments, a query is made to determine the numberof sampling cycles since hover frequency has been updated (block 720).If the number of cycles since the last update exceeds a pre-definedthreshold, e.g. a threshold of approximately 50 cycles, parameter W isset to zero (block 725) and the hover to tip threshold is initialized toits low confidence level (block 730). According to some embodiments ofthe present invention, the sampling of the digitizer sensor continueswith initialized parameters as described in reference to FIG. 5.

According to some embodiments of the present invention, a method fordetermining that output signals from a digitizer sensor results from ahovering event where the stylus is hovering above a pre-defined heightincludes determining a height of a stylus above the digitizer sensorbased on analysis of a pattern of signal amplitudes obtained from thedigitizer sensor. Reference is now made to FIG. 8 showing an exemplaryflow chart of a method for updating frequency associated with hover inresponse to detected height of stylus in accordance with someembodiments of the present invention. According to some embodiments ofthe present invention, upon start-up of the system, a query is made todetermine if a stylus is present in the vicinity of the digitizer system(block 910). If a stylus is present, the height of the stylus above thedigitizer sensor is calculated (block 920). In some exemplaryembodiments, the height determined is qualitative, e.g. high, medium, orlow. In other exemplary embodiments, the height determined isquantitative, e.g. measured in mm above digitizer sensor. If the stylusheight is determined to be greater than zero and/or greater than apredefined threshold (block 930), the frequency of the detected signalis compared to a previously defined hover frequency (block 940). If thehover frequency is other than the previously defined hover frequency,the define hover frequency is updated (block 950). Otherwise thepreviously defined hover frequency is maintained (block 960) and thecycle is repeated for a subsequent sample. In some exemplaryembodiments, hover frequency is updated based on the methods describedin reference to FIG. 6. In some exemplary embodiments, the threshold forstylus height is set at a value above zero, e.g. 1-2 mm, to avoid errorsin hover detection at low hover levels. In some exemplary embodiments,the threshold for stylus height is set at a value above zero, e.g. 1-2mm for low confidence levels of hover frequency and set at zero for highconfidence levels of hover frequency.

Reference is now made to FIG. 9A showing simplified patterns of signalmagnitudes corresponding to hovering at different heights in accordancewith some embodiments of the present invention. The pattern of signalmagnitudes shown in FIG. 9A correspond to expected outputs fromindividual conductive lines as opposed to outputs from differentialamplifiers described in FIG. 2. According to some embodiments of thepresent invention, pattern 810 corresponds to a stylus tip touch in thevicinity of the 30^(th) conductive line, while pattern 820 and 830correspond to a stylus hovering over a digitizer at a medium height,e.g. 8-10 mm above digitizer sensor, and a low height respectively, 3-5mm above digitizer sensor.

Reference is now made to FIG. 9B showing similar patterns of signalmagnitudes corresponding to hovering at different heights obtained fromoutputs of a differential amplifier according to some embodiments of thepresent invention. In some exemplary embodiments, outputs fromdifferential amplifiers may typically include a dip, e.g. dip 850, in apeak amplitude pattern, due to canceling out of a signal appearing onboth inputs to the same differential amplifier. In FIG. 9B, a stylus tiptouch signal results in the highest signal amplitude pattern in thevicinity of the 20^(th) conductive line while a signal amplitude pattern870 and 880 in the vicinity of the 30^(th) conductive line correspondsto medium and low hovering respectively as described in reference toFIG. 9A. In some exemplary embodiments, dips in the hover signal mayalso appear.

The present inventors have found that data relating height of a stylusto a pattern of signal magnitudes across a plurality of conductive linesof the digitizer sensor may be fitted to a polynomial defining height asa function of the ratio between amplitudes of signal outputs. Accordingto some embodiments of the present invention, height is defined as afunction of a ratio between the sum of pre-determined number of largestamplitude values, e.g. four largest amplitude values, and the sum ofamplitude values from all the sensor lines and/or all sensor lines in apre-defined area. According to some embodiments of the present the ratiois defined as:R=(AMP _(max1) +AMP _(max2) +AMP _(max3) +AMP _(max4))/ΣAMP _(i).

Where (AMP_(max1)+AMP_(max2)+AMP_(max3)+AMP_(max4)) is the sum of thefour highest amplitude readings and

ΣAMP_(i) is the sum of all the amplitude readings.

Alternatively, a summation of all the readings sampled in a defined areaaround the four highest readings may be used. In some exemplaryembodiments of the present invention, the relationship between theheight of the stylus and the ratio is defined by polynomial:Height=a*R ³ +b*R ² +c*R+d;It is noted that other polynomial functions can be defined relatingheight to the ratio, R.

Where the pre-defined constant coefficients of the polynomial aredefined based on experimental values and saved in the system's memory.Alternatively, the pre-defined coefficients may be a function of theratios. It is noted that although a third order polynomial is defined,other orders of polynomials may be used, e.g. second order, fourthorder, or fifth order polynomial may be used.

Reference is now made to FIG. 10 showing an exemplary flow chart of amethod for determining a stylus' height above a digitizer sensor from apattern of signal magnitudes detected on the digitizer sensor inaccordance with some embodiments of the present invention. According tosome embodiments of the present invention, for outputs indicating thepresence of a stylus (block 910), signal outputs from all the conductivelines of the digitizer sensor are sampled and their amplitude isdetermined (block 1020). According to some embodiments, four sensorlines representing the four highest amplitude readings are selected andtheir values are summed (block 1030). In some exemplary embodiments, thefour sensor lines selected are required to be proximal to each other,e.g. within 8 contiguous sensor lines. In some exemplary embodiments,more or fewer than four amplitude readings are used, e.g. a summation ofthe 3 or 5 highest readings are used. According to some embodiments ofthe present invention, a ratio is determined between the sum of the fourhighest readings and the sum of all the readings sampled (block 1040).According to some embodiments of the present invention, height of thestylus is calculated (1050) based on the pre-defined polynomial.

The present inventors have found that although the amplitude of theoutput signal varies as a function of the height of the stylus above thedigitizer sensor, the amplitude of output signal is also a function of astylus' position with respect to the sensor conductive lines on thedigitizer sensor. For example, when the tip of the stylus is orientedand/or aligned directly over a conductive line the amplitude of theoutput signal is typically greater then when the tip of the stylus isaligned in between two sensor lines. According to some embodiments ofthe present invention, the positioning and/or alignment of the styluswith respect to the most proximal sensor lines is determined andconsidered when estimating the height of the stylus over the digitizer.According to some embodiments of the present invention, two differentratios are determined so that both amplitude variation due topositioning of the tip of the stylus at a distance between two sensorlines and amplitude variation due to height of the stylus above thedigitizer can be considered.

Reference is now made to FIGS. 11A-B showing simplified graphs ofexemplary outputs from three conductive lines of a sensor for differentpositions of the stylus along the digitizer sensor when the stylus isheld at two different heights in accordance with some embodiments of thepresent invention. In FIG. 11A, representative outputs 1130, 1150, and1170 from three consecutive sensor lines N−1, N, and N+1 is shown.Outputs shown in FIG. 11A represent outputs obtained from a styluspositioned at a height H1 over the digitizer sensor. In FIG. 11B,representative outputs 1135, 1155, and 1175 from three consecutivesensor lines N−1, N, and N+1 is shown. Outputs shown in FIG. 11Brepresent outputs obtained from a stylus positioned at a height H2 overthe digitizer sensor. Since both height of a stylus above the sensorsurface and position of the stylus with respect to sensor line N affectthe amplitude of the output, the same outputs can be obtained for adifferent height when the stylus is at a different distance from sensorline N. According to some embodiments of the present invention, tworatios are determined to resolve the ambiguity in height above adigitizing surface for different distances of a stylus tip from a sensorline N.

Typically, when the stylus tip is positioned directly over a sensor lineN, a maximum output, 1111, is obtained from line N for a given heightabove the sensor and outputs 1112 from contiguous lines N−1 and N+1 maybe substantially the same and lower than output 1111. As the stylus tipis distance from line N, either to the right or to the left, the outputfrom line N decreases in a substantially symmetrical manner and outputfrom lines N−1 and N+1 will increase or decrease depending on thedistance between the stylus tip and the sensor line. For example, if thestylus is moved to position A away from line N and further away fromline N−1, a lower output 1150A is obtained from line N and a loweroutput 1130A is obtained from line N−1. However, a higher output 1170Amay be obtained from line N+1 since the stylus tip is now closer to lineN+1.

As can be seen in FIG. 11B, a similar relationship between outputs ofdifferent lines exists although the amplitude of the output signal fromthe sensor lines at height H2 are generally lower than outputs signalsfrom sensor lines at height H1. Typically, as the height increases, theamplitude of the output decreases so that H2 is above height H1. In someexemplary embodiments, the shapes of the curves, e.g. curves 1130-1175,may also differ for different heights, e.g. as described in reference toFIG. 8A.

According to some embodiments of the present invention, changes inamplitude variation due to positioning of the tip of the stylus at adistance between two sensor lines and amplitude variation due to heightof the stylus above the digitizer is distinguished by examining twodifferent ratios of amplitudes from three contiguous sensors, where themiddle sensor line from the three exhibits the highest output in thedigitizer sensor. In some exemplary embodiments, a first ratio comparesamplitude output from lines N−1 and N+1 and a second ratio comparesoutput from line N and N+1. Alternatively, the second ratio may compareoutput from line N and N−1. Optionally, three ratios are examined, e.g.N+1/N−1, N/N+1, and N/N−1. Optionally, the first ratio compares a sum ofamplitudes from a pre-defined number of contiguous sensor lines on oneside of N and a sum of amplitudes from a pre-defined number ofcontiguous sensor lines on the other side of N.

According to some embodiments of the present invention, the first ratio,e.g. (N+1/N−1) is most sensitive to the position of the stylus tip inbetween the three sensor lines. In some exemplary embodiments, a ratiothat is substantially one indicates that the stylus tip is positioneddirectly over sensor line N, e.g. with a zero distance between sensorline N and position of the stylus tip, while a ratio that is greaterthan one indicates that the stylus tip is closer to N+1, and a ratiothat is less than one indicates that the stylus tip is closer to sensorline N−1.

According to some embodiments of the present invention, the second ratiois most sensitive to the height of the stylus. In some exemplaryembodiments, for lower heights of stylus, e.g. when stylus is neardigitizer surface, difference between N and N−1 generally increaseswhile for higher heights of the stylus, differences between N and N−1generally decrease.

According to some embodiments of the present invention, two look uptables are saved in the digitizer system's memory. A first table chartsdistance of the stylus tip with respect to sensor line N as a functionof the first ratio and the height of the stylus tip. According to someembodiments of the present, a second table charts distance of the stylustip with respect to sensor line N as a function of the second ratio anda height of the stylus tip. According to some embodiments of the presentinvention, values from the first and second table are experimentallydetermined by calculating rations from detected output while positioninga stylus at different positions with respect to a sensor line and atdifferent heights. Typically, a plurality of possible distances fromsensor line N may be obtained from each of the first and second tables,each distance corresponding to a different height.

Reference is now made to FIG. 12 showing an exemplary flow chart of amethod for determining a stylus' height above a digitizer sensor and itsposition in relation to conductive lines on the digitizer sensor from apattern of signal magnitudes detected on the conductive lines ofdigitizer sensor in accordance with some embodiments of the presentinvention. According to some embodiments of the present invention, foroutputs indicating the presence of a stylus (block 910), signal outputsfrom all the conductive lines of the digitizer sensor are sampled andtheir amplitude is determined (block 1220). According to someembodiments of the present invention, three contiguous linesrepresenting the highest amplitude signals are selected (block 1230).According to some embodiments of the present invention, two ratios arecalculated from the selected lines (block 1240). In some exemplaryembodiments, a first ratio between the third and first line iscalculated, e.g. the two outer lines, and a second ratio between thesecond and first line, e.g. two contiguous lines is calculated.

According to some embodiments of the present invention, each of the tworatios is compared to a look up table to determine possible positions ofthe stylus over different heights (block 1250). Typically, a first setof possible positions, x₁ is obtained from the first ratio and a secondset of possible positions, x₂ is obtained from the second ratio. Thedifferent possibilities correspond to different heights. According tosome embodiments of the present invention, ΔX is defined for eachheight, where ΔX=|x₁−x₂| and a minimum value of ΔX is selected (block1260). According to some embodiments, the position and height thatyields the lowest ΔX is determined to be the position of the stylus tipand the height of the stylus over the digitizer sensor (block 1270).

It is noted that although some embodiments of the present invention havebeen described in reference to identifying a hover event or state basedon a pattern of amplitudes formed by the signal outputs, similar methodsmay be applied to detect other events occurring in other operationalmodes, e.g. tip touch, right mouse click emulation and erasing.According to some embodiments of the present invention, at least one ofthe operational modes other than hovering, e.g. tip touch, right mouseclick emulation and erasing, are identified based on a pattern ofamplitudes formed by the signal outputs and pre-defined frequenciesassociated with each of the operational modes are updated based ondetected frequencies of the identified signal outputs.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

What is claimed is:
 1. A method for identifying that an objectconfigured for interacting with a digitizer sensor is hovering over thedigitizer sensor, the method comprising: triggering circuitry of theobject with a triggering signal to produce a response from the object;detecting the presence of the object in the vicinity of the digitizersensor from the response of the object as detected from a peak formed bysignal outputs obtained from a plurality of sensing elements of thedigitizer sensor, wherein each of the plurality of sensing elements isassociated with a different area on the digitizer sensor; identifying atleast one sensing element providing a highest amplitude signal outputfrom the plurality of sensing elements; characterizing a width of thepeak with at least one ratio between amplitude of signal output from theat least one sensing element identified and amplitude of signal outputfrom at least one other sensing element and with a defined distancebetween the at least one sensing element and the at least one othersensing element; and identifying that the object is hovering based onthe characterization of the width by comparing the at least one ratio toa threshold level for hovering, the threshold level associated with thedefined distance between the sensing elements.
 2. The method accordingto claim 1, comprising: determining frequency content of a hoveringsignal obtained from the at least one sensing element over a pluralityof cycles of sampling the digitizer sensor outputs; determining anextent of variations in the frequency content of the hovering signalover the plurality of cycles; and identifying hovering below thepre-defined maximum height of the object when the extent of thevariations determined is less than a pre-defined threshold.
 3. Themethod according to claim 1, comprising: determining frequency of thesignal outputs during hovering; and matching the triggering frequency ofthe triggering signal to the determined frequency for hovering.
 4. Themethod according to claim 3 comprising: defining a frequency foridentifying each of a plurality of operational modes; and updating thefrequency defined for identifying at least one operational mode, otherthan the hover operational mode, based on the determined frequency ofthe hovering operational mode.
 5. The method according to claim 1,wherein the at least one ratio is a ratio between a highest amplitudesignal output obtained from a first sensing element on the digitizersensor and an amplitude obtained from signal output of a second sensingelement contiguous to the first sensing element.
 6. The method accordingto claim 1 comprising determining a height of the object above thedigitizer sensor based on a pattern formed from amplitudes obtained fromdifferent sensing elements from the response produced by the object inresponse to the same triggering signal and comparing the pattern to apattern associated with a defined height of the object.
 7. The methodaccording to claim 6 wherein the height determined is a qualitativeheight.
 8. The method according to claim 7 wherein the qualitativemeasure for height includes low hovering, medium hovering and highhovering of the object.
 9. The method according to claim 1, comprisingdetermining a height of the object above the digitizer sensor, whereinthe height is a function of the at least one ratio and pre-definedcoefficients.
 10. The method according to claim 1 comprising:determining at least two ratios between amplitudes formed by the signaloutputs from different pairs of sensing elements, wherein the signaloutputs are obtained from the response produced by the object inresponse to the same triggering signal; and resolving ambiguity of theheight of the object above the digitizer sensor by comparing the atleast two ratios.
 11. The method according to claim 1, wherein theobject is selected from a group including: stylus, token, and gamepiece.
 12. The method according to claim 1, wherein the object interactswith the digitizer sensor in a plurality of operational modes.
 13. Themethod according to claim 12, wherein the plurality of operational modesincludes at least one of hovering operation mode, object touchingoperational mode, right mouse click emulation, and erasing.
 14. Themethod according to claim 1, wherein the object includes a passiveresonant circuit configured to transmit a signal in response to atriggering pulse.
 15. The method according to claim 14, wherein theresonant circuit is configured for resonating at a different frequencyfor each operational mode.
 16. The method according claim 1, wherein theobject includes a resonant circuit and at least one capacitor connectedin parallel to the resonant circuit via a user controllable switch, andwherein an operational mode of the object is selected by activating theswitch.
 17. The method according to claim 1 wherein the object is apressure sensitive stylus sensitive to pressure applied to a tip of thestylus.
 18. The method according to claim 17, wherein the pressuresensitive stylus includes a resonant circuit, wherein the resonantcircuit includes a variable element and wherein the element is varied inresponse to varying pressure applied on the tip of the stylus.
 19. Themethod according to claim 1, wherein the sensing elements include a gridof conductive lines.